Problem: $ B = \left[\begin{array}{rrr}1 & 1 & 2 \\ 1 & 1 & 0 \\ 2 & 0 & 1\end{array}\right]$ What is $ B^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}-\frac{1}{4} & \frac{1}{4} & \frac{1}{2} \\ \frac{1}{4} & \frac{3}{4} & -\frac{1}{2} \\ \frac{1}{2} & -\frac{1}{2} & 0\end{array}\right]$